Making my page responsive to devices

I seem to have the same problem over and over again.Iv finished my product landing page but im struggling to make it responsive to devices. Im kindly seeking help, heres the link: https://codepen.io/Takudzwa95/full/RzXzPe. Another issue was the video i imported from youtube just woudnt play, so that one is actually one i took from W3school. Where am i going wrong?

Thank you.